Circuit breaker



April 1 w. B. WHli'NEY ET AL. 1,955,215

CIRCUIT BREAKER Filed April 25, 1952 10 Sheets-Sheet 1 Fig. 1.

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. nv VENTORS B) 45 w ATTORNEYS Patented A r. 17, 1934 omomcr BREAKER Willis Bevan Whitney,

Edmund Basil Wedmore,

and Alexander Morris Cassie, London, England, assignors to The British Electrical and Allied Industries Research Association,

London,

England, a British company 1 Application April 25, 1932, Serial No. 607,470 In Great Britain May 9, 1931 38 Claims.

This invention relates to electrical switches or circuit breakers wherein a supply of fluid such as a liquid or gas, or a mixture of both is provided for extinguishing the are set up on interruption of the circuit. The invention has application to other circuit interrupter-s such as ligh ning arr-esters and fusible cut-outs, in which an arc may be set up at the moment of discharge or at the moment of the fuse interrupting the circuit.

It has already been proposed to provide a high tension switch having a closed casing containing an insulating liquid such as oil with a piston which is moved upon opening of the switch so as to generate pressure which is employed upon separation of the switch contacts to cause oil to flow under pressure between the arcing contacts. The present invention is more particularly concerned with switches in which the blast of fluid is driven across one electrode in this way by means of the movementof a piston.

According to the present invention, an electrical circuit breaker, switch or other circuit interrupting device has the electrodes arranged so that the are between them is struck in a confined or substantially closed arcing space and a piston or. equivalent pumping device is provided in such a way that the pressure set up by the products of the arc acts on both of its faces so as to cause the piston to move during arcing between the electrodes in order to squeeze the extinguishing fluid in that arcing space and to force 'it into contact with at least one of the arcing electrodes before escaping to the other side of the 35 piston.

Constructions of circuit brakers are already known, in which the arc products have been squeezed out of the arc gap by pressure set up independently of the arc itself. The present invention employs the energy of the are drawn between a pair of electrodes to squeeze the are products from the arc gap between the electrodes by utilizing the principle of the hydraulic press so that the gases after they have been squeezed from the arc, exert pressure upon a surface of a movable member of relatively larger area than that of the surface acted upon to oppose the movement of that member. The moving member compresses or drives fluid into the arc gap and thus may be arranged in such a manner that the part of the are subjected to the blast in the arc gap cannot escape from the region subject to the high. intensity of pressure.

A unit of a circuit breaker in accordance with 55 the invention may be arranged for mounting on invention;

the leading-in insulators of -many existing circuit breakers with little or no alteration to the existing parts. The circuit breaker may be arranged to .set up two or more breaks in series, and a series of bafile plates forming shallow chambers between them in accordance with our United States patent application Serial No. 563,- 390 dated 17th September, 1931 may be employed so that the moving switch contact moves through apertures in the baflle plates or moves past the edges of the bafile plates. The invention is not, of course, limited to switches or circuit breakers in which the electrodes are positively separated, but it may be applied to other circuit interrupters, such as fusible cut-outs, lightning or surge arresters and so forth.

In order that the invention may be clearly understood and readily carried into eiiect, a number of forms of construction of circuit interrupters in accordance therewith will now be described with reference to the accompanying drawings, wherein:-

Figure 1 is a sectional elevation taken through a diametrical plane to the left of the centre line and with the outer casing in section to the right of the centre line showing one form of construction of circuit breaker in accordance with the Figure 2 is a sectional elevation of a detail showing a constructional variation of Figure l Figure 3 is a similar view with the lower part omitted of an alternative construction;

Figure 4 is a central vertical section, and

Figure 5 a sectional plan of a construction employing a number of pistons;

Figures 6 to .12 are central vertical sections shown somewhat diagrammatically to a reduced scale of a number of modified forms of construction of circuit breakers in accordance with the invention;

Figure 13 is a central vertical section showing the invention applied to a fusible cut-out;

Figure 14 is a similar view showing the invention applied to a lightning arrester or surge interrupter;

Figures 15 to 1'7 are central vertical sections shown somewhat diagrammatic to a small scale of three further forms of construction of circuit breakers in accordance with the present invention;

Figure 18 is a central elevation of the upper part, and

Figure 19 is a plan, half in section, showing still another form of construction in which compensating pistons are mounted in the main piston;

Figures 20, 21 and 22 are diagrammatic vertical sections to a reduced scale illustrating three further forms of construction;

Figure 23 is a central vertical section showing a form of construction showing the space below the difierential piston enclosed by a telescopic container;

Figures 24 to 27 are somewhat diagrammatic central vertical sections showing a further four forms of construction of circuit breaker in accordance with the invention; while Figures 28 and 29 are two elevations at right angles showing a method of disposing the units of a three-phase circuit breaker with a double break in each phase according to the present invention; and Figure 30 is a sectional plan on the line XJQi-XXX in Figure 28.

In the form of construction illustrated in Figure 1, the lead-in insulator 1 which may be suspended from the lid of an enclosing vessel or oil tank is fixed at the bottom to an enclosure 2 generally of cylindrical form. The cylindrical wall of 2 is generally'of metal, but is encased in an outer covering 3 of insulating material, while any screw-heads are covered with insulating.com- The vm'etal wall 2 is. turned in at the bottom at 4 to receive a base 5 pound as shown at 3a.

of insulating material which is recessed centrally at the top to receive a gland 6 also of insulating material. This is free to move slightly radially and axially with respect to the moving switch contact 7, but is retained in its recess by a cover plate 8 held in position by screws. The base 5 and the associated parts are held in position by a tubular member!) screwed into theinner wall 2 of the container. The inner cylindrical wall of the member 9 forms a cylinder of reduced diameter to receive the lower disc 10 of. a trunk piston 11. The upper disc. 12 of the piston 11 slides directly within the inner surface of the wall 2. The piston 11 is normally held up in the position shown in the drawings by a rather light spring 13 which, in the position shown, is extended to its limit. The piston 11 also has a number of circumferentially spaced castellations 14 for the purpose of increasing the guiding area of the upper part of the piston and yet of allowing of access from the central space above the piston to the cylinder wall 2 for the purpose which will appear below. Of course, the castellations 14 might be used as stops for the piston stroke if they were arranged to come into contact with the metal top plate 15 of the container, but as illustrated this is not the case as the spring 13 is fully extended before that state of afiairs is reached.

. After the base parts, the spring 13 and piston 11, are placed in position, the cover or top plate 15 carrying the fixed contacts 16 may be screwed in. The contacts 16 are screwed into a depending sleeve 17 formed in two parts, the lower part 17a of which fits a bore of the piston 11 and the upper part 17b of which is screwed into arecessed plate 18 fixed by screws 19 to the top plate 15. The upper part 17b of the sleeve 17 is provided with windows 20 through whichpr'essure at the centre has access to the upper disc 12 of the piscontacts 16 to prevent the accumulation of a I pocket of gas outside these contacts. Seep holes may also be provided in the top plate 15 at 23 and in the recessed part of the plate 18 if it is desired to prevent the trapping of a cushion or pocket of permanent gas, and the seep holes 23 may be extended, for example, by tubes such as shown in dotted lines at 24 to imprison gas or vapour in the upper part of the contact when it is desired to produce a cushioning effect. Again, the seep holes may be drilled through the sides of the casing 2 and 3 at the required height for the same purpose. The container 2 is provided with an exhaust port at 25. The moving contact 7 is shown in full lines in its uppermost position corresponding to the closed position of the switch and is shown in dotted lines at 7a in the fully retracted position which it may take up when the switch is opened. Ofcourse, a wider gap between the bottom of the container 2 and the top of the moving contact 7a can be obtained when a longer stroke is available.

In operation, the moving contact 7 is drawn central passageway within the contact 16 through the windows 20 on to the top of the piston 11 within the cylindrical wall 2. As this upper surface is of greater area than the lower exposed surface there will be a downward unbalanced pressure on the piston 11 so that this will comspring 13 and forcing oil from below the piston through the central passageway in the fixed contacts 16 so that the oil will be forced across and along the surfaces at which the arc is formed. This action continues until the upper disc 12 of the piston uncovers the exhaust port 25; then any excess pressure is released and the spring 13 is enabled to raise the piston 11 again into the normal position shown in the drawings.

There are thus spaces within the switch container 2 on opposite sides of the piston 11 which may be referred to as the primary and secondary pressure-retaining chambers, each of which may, however, consist of more than one space in communication. In Figure 1, the space within the tubular member 9 below the piston 11 forms the primary pressure-retaining chamber, while the secondary pressure-retaining chamber consists of the whole of the space above the moving contact 7 within the fixed contact 16 and sleeve 17 and also that above the top of the piston disc 12. The primary and secondary chambers 'mence to move downwards, compressing. the

thus communicate with each other through one or switch contact 7 is situated in the primary chamher which contains extinguishing fluid, when the piston movement starts, the total space enclosed within the walls of the primary chamber is decreased by an amount smaller than the increase in space in the secondary chamber and this results in squeezing the extinguishing fluid so that it washes over a surface of the switch contact 7 before it escapes through the passageway in the fixed contact 16 into the secondary chamber. The electrodes are thus preferably so formed that one of them provides, at least in part, a passage through which the extinguishing fluid flows and the flow of this fluid is assisted by the pressure of the hot products from the are acting upon the upper face of the piston 11 to which they have access after they pass through the passageway in the fixed contact '16 and this pressure acting upon the upper face of the piston 11 acts against the retarding effect on the lower face of the piston of the pressure due to the hot products from the arc. When as in Figure 1, the area of the upper face of the piston is sufliciently greater than the area of the lower face, the unbalanced force exerted by the arcing products alone causes motion of the piston as described above and as a result, the oil or other extinguishing fluid is forced by the piston through the central aperture in the contact 16 and is thus forced across at least one electrode of the switch in order to extinguish the arc..

In actual practice a circuit breaker unit as shown in Figure 1 may have the following overall dimensions, viz., a height of 8 inches and diameter of 6 inches with the moving contact '7 having a diameter of 7 of an inch. It was found that with such a construction, a series of seven repetition tests resulted each time in the successful interruption of a highly inductive circuit carrying an alternating current of 500 R. M. S. amperes at a frequency of 50 cycles per second derived from a power transformer stepping up from 6600 volts to 22,000 volts and giving a recovery voltage of 21,000 volts across the single gap employed. The gap between the contacts '7 and 16 was limited to 0.8 inches and the largest arc gap at arc extinction was 0.34 inches. All tests were cleared in less than one cycle of arcing. In some cases the arc was extinguished before the separating-contacts 7 and 18 had, formed a gap of 0.2 inches corresponding to a dielectric strength of over 100,000 volts per inch. As an indication of the improvement attained by this method of arc rupture as compared with a plain break in oil, it may be mentioned that in the latter case, arcs of upwards of 10 inches in length would be drawn with the same applied voltage and current per break, giving an are energy output many times greater than that liberated in the above seven tests with a current breaker in accordance with the present invention. In these tests, the unit was completely filled with oil except for a small cushion of approximately 7 c. c. trapped in the top contact holder 17?) and the head of oil in the outer tank, surrounding the arcing container 2, measured upwards from the top of the exhaust port 25 was 5 inches in the first five tests and 9 inches in the last two. The average piston travel during the first 1/50th second after commencement of arcing was of an inch.

The limitation of the gap between the electrodes was obtained by stopping the movement of the moving electrode 7 while allowing it to remain in electrical contact with the moving cross bar by way of an extensible connection. A somewhat similar method of obtaining a limited gap without interference with the straightthrough movement of the cross bar of a circuit breaker will be described below in connection with Figure 17. As pointed out in the specifications of our United States patent applications Serial No. 180,204 filed 1st April, 1927, and Serial No. 411,307 filed December 3, 1929, the use of a short gap is advantageous as it reduces the length and energy of the are within the gap to a minimum so that the arcing surfaces of the counter contacts can be kept in a region where the fluid blast flows into the gap at high velocity and thus efficiently scours away the hot products of the minimized are energy and cools the arcing surface. Thus, when the current, in its alternation, reaches zero, conditions of temperature and fluid density are set up which prevent the applied voltage from restriking across the gap subsequently thus extinguishing the are.

In order to prevent knock at the end of the stroke and to ensure that the stroke of the piston lasts for two cycles or more in order to secure a sufficient duration of blast for the extinction of the are within a cycle and to provide an adequate factor of safety, it is desirable in some cases to introduce a dash-pot effect.

One method of doing this is illustrated in Figure 2, which illustrates a modified construction of the circuit breaker shown in Figure 1 and only includes the portion round about the exhaust outlet 25. The upper part 12 of the piston 11 in this case has a depending edge portion 12a which during the first part of the downward stroke gradually closes the main exhaust outlet 25 so that the oil between the outer cylinder 2 and the wall of the piston 11 has from that instant to escape through an auxiliary outlet or outlets 25a in the wall 2 of the container so as to produce a dash-pot effect. Towards the end of the stroke and before the lowermost outlet 25a is covered, the top of the piston 11 uncovers the outlet 25 allowing of exhausting of the products above the piston 11. A small hole or passage 9a is also provided in the tubular member to allow a rapid start off of the piston 11. The remaining reference numerals are as in Figure 1 so that the construction can be clearly appreciated.

In Figure 3, the construction is shown slightly modified in the upper part, but the same in the lower part as in Figure 1. In this case, the piston 11 itself carries the relatively fixed contacts 16 and consequently provision has to be made to carry the current to these contacts. This is effected by means of a series of flexible leads 26 serving as pigtails and clamped by screws at the upper end to the plates ,18 fixed to the top metal plates 15.

The action in this case is similar to that in Figure 1, except that when the piston 11 moves downwardly, the contacts 16 move with it, but, as explained below, not as rapidly as the moving switch contact 7. Thus, when the are products pass out from the exhaust port 25 and the piston 11 rises again, it carries up with it the contacts 16 thereby increasing the separation between them and the moving contact 7.

The form of construction described will tend automatically to keep the gap short because if the lower contact moves down much quicker than the nozzle contact carried by the piston the increased length of arc will lead to the generation of increased pressure and hence to a greater difference of force on the two sides of the piston so that the latter will be accelerated downwards.

If, however, owing to excessive length and are energyof the arc, the moving piston 11 with its contact 16 begins to overtake the moving contact 7, the length of the arc and hence its energy, is decreased so that the downward force on the outer piston is decreased and it tends to lag behind again. If, alternatively the reduction in length is so fast that there is not time for the reduction in are energy to affect the piston, the nearer approach of the opening in the contact 16 to the end of the electrode 7 will produce a throttling effect on the escaping oil which will become more and more powerfulas the two electrodes approach one another and, since the only means for escape of the oil or other fluid fromv the arcing chamber is through the contact 16, this throttling action will itself slow down the rate of movement of the piston 11 and allow the moving contact 7 to draw away from it again. The arrangement thus'constitutes an example of a self-adjusting arc gap. The adjustment may be further modified by the relative shaping of the counter electrode surfaces .so as to produce either a rapid or slow throttling for given rate of linear approach.

It is, of course, important for the downward 'movement of the piston and consequently the forcing of oil through the passageway in the contacts 16 not to be delayed due to unnecessarily high inertia of the moving parts or other cause. A form of construction is shown in Figures 4 and 5 which is designed to reduce the time taken in the pistons starting. In this construction the container 2, connected to the lead-in insulator 1 and lead 21 and having a covering 3, is of much the same form as before, being flanged at the bottom at 4 and receiving the base members 5, 6 and 8. In this case, however, instead of the tubular extension 9 a clamping ring 2'7 is screwed into the container to hold the base components in position. Furthermore, the container 2 is internally shouldered at 2a and a cage 28 is inserted from the top to rest on the shoulder 2a. This cage may be a casting bored to receive a number of pistons 11; for lightness these pistons are hollow and may be closed at the bottom by plugs 11a which also act as stops for the pistons at the upper end of their strokes. The whole cage is held in position by a screwed-in ring 29. In this case, the fixed contacts 16 are screwed into the inner bore .of the cage 28. The pistons are shouldered, the

external cross-sectional'areas of their stems presenting the end surfaces exposed to pressure below the contacts 16 and upper disc 12 of greater area being exposed to the pressure above the contacts 16. Seep holes are provided at 22 and 23 as is Figure 1. Each piston 11 has its own independent spring 13. In this case, when the moving contact "7 is moved downwardly and an arc is struck between it and the fixed contacts 16, the

pressure acting on the greater area at the top of each piston 11 causes it to move down quickly against the springs 13 as the pistons are made very light and thus oil is forced rapidly into and through the passageway in the contacts 16, and this goes on until the disc 12 uncovers the exhaust ports 25. These ports all open into an annular manifold 30 which itself opens at one part of the circumference by way of a port 31 through the container wall 2 and insulating cover 3 into the outer oil tank. In Figure 4, also, the contact 16 is shown with a diverging exhaust funnel so as to assist the rapid escape of the hot gases from the arc gap.

In the form of construction illustrated in Figure 6, the piston'll has its upper part 12 sliding in a cylinder formed by a downward extension 24 from the cover 15 of the container 2, while the lower part 10 of the piston 11 slides in the lower part of the container 2. The moving contact '7 has its upper part hollow and in communication with the space below the piston 11 through lateral ports 35. The fixed contact 16 is supported in a central insulating disc 36 screwed into the cover 15 and is connected to the lead-in conductor passing through the insulator 1. In this case,

when the arc is struck between the contacts 7 and 16, the pressure set up acts directly on the top of the piston 11 and is transmitted through the hollowbore of the upper part of the contact 7 to the space below the piston where it acts on a larger efiective area. The piston is therefore, forced upwards telescoping into the cylindrical extension 34. Owing to its shape it sweeps all the oil and products of arcing completely out from the inside of the cylinder 34, the products passing through the contact '7 to the space below the piston and ultimately through the exhaust port 25, when the piston 11 has risen far enough to uncover that port. When the pressure below the piston is exhausted, the circuit interrupted and the arc extinguished, the piston 10 is reset due to its own weight. This resetting by gravity has an advantage, in cases in which it is desirable that there shall not be an increasing retardation of the piston as it travels forward as.

would be the case if the piston moves against the action of a spring.

Figure 7 illustrates another telescoping arrangement providing rigid walls for the arc chamher and a rigid outer container. In this form of construction, the whole unit is extremey compact and increases its length downwardly during the arcing process and subsequently is shortened again. As before, the'container 2 is shown with the insulator 1 with the lead-in conductor mounted on the cover 15. The piston 11 has a tubular extension 36 which slides downwards with the lower plate 37 of insulating material, through which the movable contact '7 can slide.

The products of arcing act on the whole of the upper face of the piston 11, but only on the central part of the lower face. The upper contacts 16 are carried by the piston and are connected to the lead-in by pigtails 26 as in Figure 3 so that the method of operation is very similar to that of the form of construction shown in Figure 3.

It will be seen that in the type of construction illustrated in Figure '7, the overall height of the container 2 for given length of the piston stroke is much less than in the constructions already described. The downward extension in length during arcing can take place quite conveniently in this construction, even in the usual case in which the moving electrode 7 is carried on a cross-bar, since the cross-bar movement will be in the same downward direction. After the arc has been extinguished, the extended wall 36 is retracted back into the reatively short cylindrical container 2, as mentioned above. Thus. for a given stroke of cross-bar and piston and for a given distance between the insulator 1 and the cross-bar in the full open position of the switch. this construction allows a larger clearance between the cross-bar and the bottom of the container 2 than do the constructions already described. Longer clearance; of this kind are advantageous as they make it easier at given voltages to prevent or minimize corona discharge which might otherwise takeplace where the overall clearances within which the container has to be fitted are small.

This form f construction also illustrates a method of combining certain of the advantages of the downwardly extendabe construction with a self-adjusting arc gap as illustrated in Figure 3 and with the further useful feature that the external sliding surface of the cylinder 11 is open to inspection and cleaning without opening up the container 2.

In Figure 8 a construction is shown which in general is similar to Figure '7. This construction,

however, has certain advantages in that it allows of inspection of two sliding surfaces and of the spring 13 without opening the container 2; also, it may be fitted with an auxiliary contact 49a suited to provide aself-adjusting arc gap in-.

dependently of the movement of the contact 7. The auxiliary contact 49a is shown mounted on a sliding member 49 within the tubular downward extension 71. It is pressed down by a light spring 50. If now the moving contact 7 descends too quickly and there is excessive differential pressure generated, the oil forced up by the piston 11 below the member 49 will lift the latter and the arc will pass from the fixed contact 16 to the upper tip of the member 49 and then across the very small gap to the moving contact '7. The member 49 has seep holes 51 and inclined ports 52 so that the oil forced up can pass through the ports 52 and through the space between the contacts 7 and the member 49.

In Figure 9, a construction is shown in which the whole of the container 2 moves relatively to the fixed insulator 1 and the piston 11, which has attached to its lower surface a metal bellows or springy tube 39 and this figure illustrates a type of construction particularly suited for the separation and complete ejection of the dirty used oil from the container 2 and from the outer switch tank in which the container may be immersed. The bellows 39 may conveniently be made of thin metal such as rustless steel or tombac. As a matter of fact, in Figure 9, arrangements are shown for ejecting the used oil through the centre of the insulator 1. When the arc is struck between the contacts 7 and 16, the pressure within the bellows 39 acts on the central part of the underneath face of the piston 11 and the pressure also acts on the top of the piston 11, which, as already mentioned, is in this case, fixed to the lower part of the insulator 1 and cannot move. A thimble-shaped valve 40 is lifted by the pressure against a light spring 41 and it enters the lower part of the tubular member 95 with the result that its ports 42 are cut off. The differential pressure, therefore; is able to lift the whole container 2 against the return spring 13 so that the space above the piston 11 increases in volume and that within the bellows 39 decreases squeezing the oil out through the upper contacts 16. As soon as the top of the casing 2 rises above the exhaust port 13, the pressure above the piston 11 is exhausted between the inner and outer tubes 97 and 98 and thence for example, through a nonreturn valve or swan-neck, not shown, to a drain,-

and the spring 13 is able to push down the container 2 again. During this time, the volume within the bellows 39 increases so that the bellows expand and the valve 40 is drawn down. At the same time, the space above the piston 11 is decreasing so that any remaining used oil is forced out through the ports 42 and through the tube 9'7 to the drain already mentioned.

In a further form of construction illustrated in Figure 10, the general arrangement is very similar'to that of Figure 3, except that the upper contact 16 is not hollow and the piston 11 carries a series of bafile plates 44 which are somewhat similar to those set forth in our United States patent application Serial No. 563,390, filed 17th September, 1931. The remainder of the construction is somewhat similar to that shown in Figure 3 and the same reference numerals have been employed. When the switch is opened and the contact '7 descends, an arc is struck between it and the upper contact 16. The are products move in one general direction through the chambers between the baffle plates 44 into an axial passage 45 and the pressure is thus communicated to the whole upper surface of the piston 11. The pressure acts on asmaller area below the piston so that the latter is forced downwards against the spring 13, but the moving contact 7 moves more quickly, drawing the are past the openings between successive baflle plates- In this case, asin all the cases in which the upper contact 16 is carried on the piston, there is an effect of a selfadjusting arc gap because if the piston moves down too quickly following the contact 7, the

pressure is automatically reduced tending to make somewhat similar to those set forth in our said United States application Serial No. 563,390. In this case, however, they are inclined instead of being horizontal to provide easy flow of the fluid and are stationary, being mounted on the tubular extension 17 from the cover 15 instead of being mounted on the piston 11 as in Figure 10. The baffle plates 44 are provided with conducting tips 46. The action therefore as the contact '7 moves down is as follows:-An arc is first struck between the contacts 7 and 16;.after the tip of the contact 7 has passed the uppermost conducting tip 46, the arcing is transferred to that tip due to the action of the fluid blast acting through the passageway 48 so that then there are two arcs in series one between the contact 16 and the tip 46 and the second between the latter and the contact 7. An additional series are is formed in a similar way as the contact '7. passes each of the conductive tips 46 and the arcs which are anchored to the conducting tips 46 and cannot escape through the outlet passages are subjected to a scouring and squeezing action due to the movement of oil under pressure between the baffle plates 44. a The outer ends .of the passages between the baffle plates 44 are controlled by the piston 11 so that the outlet is varied and increases as the piston 11 descends under the action of the resultant differential pressure upon it. There is, therefore, a tendency for the outlet to open more quickly for heavy currents than for small currents. The oil below the piston 11 is thus forced through ports 47 to the inside of the sleeve 17, through ports in the insulating plate 48, across the arcing surface of the electrode 7 and through the bafiie chambers to the top of the piston 11, being ultimately exhausted through the exhaust port 25.

Figure 12 shows another construction in which the movable electrode 7 moves through a series of baflle plates 44 similar to those shown in said United States application Serial No. 563,390. The pressure from the arc passing through the baffie passages acts on the upper face of the piston 11 and the only back pressure is that acting on the lower edge of the piston. The piston, therefore, is forced down against the spring 13 and oil surrounding the contacts 7 and 16 is squeezed out through the passages between the insulating bafile plates 44. 1

Figure 13 illustrates the invention in its application to a fusible cut-out. The device has a container 2 and an upper cover 15, as before, and

a differentially operating piston 11 which under the differential pressure set up on interruption of the circuit is forced down against a spring 13. The piston, slides on the inside of an inner cylinder 53 and also onan inner insulating casing 54 which houses the fuse wire 55 extending between terminal blocks 56 and 57. The casing 54 has baiiled windows 58 through which the pressure set up by the interruption of the circuit acts on the upper and lower faces of the piston 11. The movement of the piston forces oil through the lower window 58 into contact with the fuse wire at the point of rupture. The lower contact block 57 is engaged by spring fingers 59 electrically connected to the lead-in 60 and the whole is mounted on the insulator 1. 'In order to renew the fusible element 55, the inner casing 54 is unscrewed from a partition 61 to which the other lead 60a is attached and the complete central unit lifted out by the handle 62 carrying the top cover 15 with it.

In a similar way, Figure 14 illustrates the invention applied to a lightning arrester or surge interrupter. The high tension line is carried through an insulator 1 and the -whole device is mounted in a container 2 which houses an inner cylinder '53 within which the difierentially acting pistonll slides. The electrodes 63 are shown as spherical electrodes but can obviously be of any type, for instance, plug and socket electrodes although in a surge or lightning arrester, they would not normally be in contact. The upper electrode is surrounded by a sleeve 64 preferably of insulating material. This sleeve 64 if connected by an extensible connection to the incoming lead 21, could be made in the form of a tubular contact, in which case the piston 11 or the cylin der 33 would be of insulating material. I

In this case, the descent of the piston 11, in addition to forcing oil over the surfaces of the electrodes and out through the sleeve 64, causes an increased separation of the electrodes because the lower part of the piston 11 presses on a spider 65 which descends against the action of-a spring 66 carrying with it the lower electrode 63. When the piston 11 uncovers the exhaust port 25, the pressure above the 'piston is relieved and the spring 66 is able to return the lower electrode 63 into the normal position, as shown. The insulator 1 passes through a protecting hood 67 and the lead-in conductor may be connected to the high tension line, if desired, through a limiting resistance, which, alternatively may be connected in series with the lead 68 and earth. The

connection from the lower electrode 63 to earth The piston 11 is a composite piston, the upper part 72 of which is insulated from the lower part as shown by a ring 73 of insulating material.-

Upon opening circuit, the spring 71 first keeps the intermediate contact 69 down against the and through ports 75 to the internal upper surface of the piston 11 itself. The differential pressure causes the piston and its member 72 to rise against the action of the spring 13 thus forcing oil through the ports 75 over the arcing surfaces of the contacts 16 and 69. At this stage, the contact 79 meets its stops so that the continued movement of the movable contact 7 causes the latter to leave the contact 69 thus striking a lower arc. A part of the oil now passes the spider and under increased pressure passes through the hollow bore of the movable contact 7' and out through lateral ports to the space below the piston 11 thereby increasing the upward pressure on the latter. When the piston 11 rises above the exhaust port 25, the pressure below the piston is relieved. At the same time the roof portion of the piston member 72 has risen above the additional ports 25a and the are products in the upper part are able to escape through the hollow upper portion of the depending sleeve 17 and out through outlets 25b in the top plate. The piston is afterwards reset by the spring 13 or by gravity.

In a modified form of the construction illustrated in Figure 15, the intermediate contact 69 with its spider 70 and light spring 71 may be omitted. In this case the moving contact 7 makes direct contact within the fixed electrode 16 and the passageway in contact 7 is extended downwards further than shown in Figure 15, and the outlets from the passageway are placed lower so as to allow venting to take place first below the insulating barrier a when the moving contact 7 is just leaving the contact 16.

The action upon separation of the electrodes is then as described above, except that the are products immediately escape towards either end of the enclosure through the passageways in the contacts 16 and 7 and oil or other extinguishing fluid is squeezed into the arc gap from all sides by the action of the pressure upon the ends of the differential piston ll-and its upper member Figure 16 illustrates another form of construction but making use of a double bellows. This construction employs a convenient method of venting clear of the guide surfaces which can be used in place of the ports 25 used in the solid type of constructions so far illustrated, and also employs means for minimizing the surface area of the guiding surfaces, and the entire guiding surfaces are arranged so that they are not subjected to the action of the are products and are open to inspection without opening the arcing chamber or upper container. In this case, metal bellows are attached both to the upper and lower surfaces of the piston 11 to produce the differential areas on its opposite surfaces. This enables a containing vessel to be entirely dispensed with and the piston 11 is furnishedwith lugs or ears 76 which are guided on outside guide rods 77. Springs 78 also encircle these guide rods 77 and press the piston 11 up into the position illustrated. The guide rods 77 are secured to the upper plate 79 and the lower plate 80 of the device, the whole device being carried from the lead-in insulator 1 to which the upper plate 79 is secured. In this case, the upper contact 16 is carried by the piston 11 and is a hollow contact as in many of the previous forms of construction illustrated. It is connected to the leading-in conductors by pigtails 26 and between it and the pigtails, a number of metal plates or discs 81 are mounted. The purpose of these is to cool the products from the arc andcondense any vapour to prevent it being deposited on the inner walls of the upper bellows 82.

In operation, the movable contact 7.descends when the switch is opened; the pressure of the are products acts directly on the lower surface of the piston 11 and passes through the upper Contact 16 and between the discs 81 so as to act on the top surface of the piston. The piston consequently descends, extending the upper bellows 82 and compressing the lower bellows 83 and so squeezing the oil in the latter between the arcing surfaces of the contacts 7 and 16 into the space enclosed by the upper bellows 82. In this case, the piston cannot itself uncover exhaust ports, therefore, in order to exhaust the pressure from the upper space without providing ports in a guiding surface, small non-return valves 84 are provided normally spring-closed. At the lower end of the stroke, however, these valves abut against a corresponding number of studs 85 and the valves are thus opened, relieving the pressure in the upper bellows 82, whereupon the spring '78 is able to raise the piston again into the position shown in the drawings.

The form of construction shown in Figure 17 also employs bellows and this construction is particularly adapted for use when an extinguishing fluid such as hydrogen or helium is employed which it is desired to conserve. The circuit breaker in fact is completely sealed, the working spaces for the fluid being of annular shape and each lying between a pair of bellows. The stationary parts of the apparatus consist of the lead-in insulator l with its stem 1a and upper and lower plates 79 and 80 insulated from each other by the insulating cylinder 17. The rest of the apparatus rises against the action of the spring 13 upon interruption of the circuit. The upper bellows 82 and 82a enclose an annular space while the lower bellows 83 and 83a enclose an annular space of smaller cross-sectional area. When the circuit is opened, pressure from the arc between the contacts 16 and 7 passes through metal plates or discs 81, similar to and for the same purpose as those shown in Figure 16, into the annular space between the bellows 82 and 82a. The pressure is also transmitted through passages 86 in the plate 80 to the annular space between the lower bellows 83 and 83a so that the structure is raised against the spring 13 by the differential pressure acting on the plates 79a and 80a. The upper bellows 82 and 82a are thereby extended and the lower bellows 83 and 83a contracted so that fluid in the lower space is squeezed out and forced up between the arcing surfaces of the contacts into the space between the upper bellows 82 and 82a. When the arc is extinguished and the gas has cooled, the pressure subsides and the spring 13 presses down the whole structure into the position shown in Figure 17. It is clear that the movable contact 7 has to slide without allowing of any leakage from its arcing surface to the exterior. The contact 7 is therefore flanged at 7a and the flange is connected to the plate by an internal bellows 87. This bellows expands when the contact 7 moves downwards without breaking the seal between the inside of the structure and the outside. Electrical connection to the contact 7 is maintained by spring fingers 88attached to its base and carrying blocks 89 which slide over a contact rod 90 attached to the tcross-baror outgoing lead. A short stroke of the 1. In Figure 17 also, the immediate walls of the arc-- ing chamber are allowed to expand slightly although the gross volume of the arcing chamber, including in this case the volume within the double bellows 83 and 83a, is reduced to cause fluid to be squeezed into the arcing space. An action of this kind is useful in some cases as it allows dissipation of some of the initial high pressure when an arc starts in a confined space while it allows steady movement of the piston for compression purposes.

In Figures 18 and 19, the constructions shown in Figures 3 and 4 and 5 are combined in that there is a main piston 11 sliding within the container wall 2 and returned to the normal position shown by a spring 13, and in addition there are a series of hollow light pistons 11a mounted to slide in the main piston 11. Each of these pistons is provided with its separate returning spring 13a. In this case when an arc is struck, the pressure on the top of the pistons first depresses the light pistons 11a due to their lesser inertia and gives a rapid start off and a quick projection of oil through the passageway in the contacts 16 and later the main piston 11 gets into motion compressing the spring 13 and this goes on until the piston 11 uncovers the exhaust port 25, whereupon all the pistons are returned under the action of their springs into the normal position shown in Figure 18.

In Figure 20. a further form of construction is illustrated in which the differential pressure moves the piston 11 upwards and after exhausting through the ports 25, the piston is restored by its own Weight. In this construction, the container 2 has a telescopic lower extension 91 providing a long closed passage for the moving contact 7 without unduly lengthening the main part of the container 2. The piston 11 slides within the container 2 and its tubular extension slides within a downward extension 17 from the cover 15. Thus. s

when an arc is struck between the contacts 7 and 16, the pressure generated acts on the inner an nular part of the upper surface of the piston 11 and is transmitted through the hollow bore of contact 7 and through the ports 92 so as to act upwardly on the whole of the underneath surface of the piston. The piston therefore rises, squeezing the oil within the space inside the piston 11 and, inside the extension 17 across the arcing faces of the contacts and down through the centre of the contact 7. When the piston 11 rises above the exhaust port 25, the pressure below the piston is relieved and the latter can return due to its own weight. 7

In the further form of construction shown in Figure 21, the piston 11 also moves upwards under the differential pressure and is guided in a manner somewhat similar to that in Figure 20, but

its inner edge slides up over a further downward extension 93 from the cover 15, which extension' carries the hollow fixed contact 16. In this case, the moving contact 7 moves down through a series of baffle plates 44 which'are arranged to have an outlet to one side, viz., on the left of Figure 21 in a manner similar to that set forth in our said United States application No. 563,390. When the contacts 7, 16 are separated and an arc struck, the pressure passes-through these lateral outlets and the baffle plates 44 into contact with the whole of the underneath surface of the piston 11 and it also passes up through the hollow contact 16 through the ports in the top of the member 17 to the annular surface on the top of the piston 11. The piston is therefore forced up exactly as in Figure 20, but in this case the oil passes through the ports in the member 17 and down through the hollow contact 16. The construction shown in Figure 21 also allows of a relatively long piston stroke, with only a short stroke of the moving electrode 7 within the arcing enclosure.

Another form of construction is illustrated in Figure 22 embodying another method of obtaining a quick initial movement of the piston and employing a thin metal bellows 39. The construction is otherwise very similar to that shown in Figure 3, as the upper contacts 16 are mounted in'the piston 11 which moves downwards against the spring 13. The contacts 16 are connected to the lead-in conductor by pigtails 26. In this case, the bellows 39 are generally of conical shape increasing in diameter towards the bottom. The result is that a relatively rapid initial action is obtained because at the commencement of the stroke of the piston, the upper part of the bellows 39 is collapsed relatively rapidly and quickly forces oil between the contacts. Just as in Figure 3, when the pressure above the piston 11 is re leased through the exhaust port 25, the spring 13 raises the piston 11 again into the position shown. I

In Figure 23, a variation is shown in which the piston can be made to accelerate if required and in which instead of the bellows 39, a series of telescoping members 94 is employed; otherwise the arrangement is much as shown in Figure 22. In this case, therefore as the piston 11 is pushed down, the members 94 telescope in succession into one another. In this case, there is an additional optional feature shown, that is to say, the piston 11 is shown with a depending extension 12a. similar to that shown in Figure 2 and for a similar purpose; an auxiliary exhaust outlet 25a is shown so that near the bottom of the stroke of the piston 11, the main exhaust port 25 is covered and a manner somewhat similar to that shown in Figure 9. In fact, these constructions are also adapted for ejecting the dirty used oil at the top of the structure and for that purpose, although it is not shown, parts similar to 40, 41, 43, 97 and 98 in Figure 9 would be fitted. In Figure 24, the greater part of the contents of the arc chamber the port 25 isarranged at a lower level so as not to rise above the disc of the piston 11.

In Figure 25, the construction is somewhat different, as the piston 11 extends right down to the bottom of the container 2 and itself is enclosed at the bottom by the insulating disc 96 which therefore remains stationary. In this construction, when the container'2 has reached the top of its stroke, its top passes to the middle of the wide port 43 in the supporting stem 95 and therefore the space above the. piston can exhaust around the edges of the top of the casing 2 through the port 43 direct to the outside space.

A further form of construction is shown in Figure 26 which is somewhat similar to that shown in Figures 7 and 8 and here also no flexible connection or pigtail is needed. The whole container 2 moves downwards under the differential pressure against the spring 13 so that the construction forms a compact unit able to lengthen downwards during interruption of the circuit and to recover afterwards. When an arc is struck between the contacts 7 and 16, pressure acts not only on the central part of the cover 15 of the container 2, but also passes through the bore of the contact 7 s and through the ports 92 to act on the whole of the surface of the lower Wall 4 of the container This sets up the differential pressure causing Exhaust takes place after the arc- In Figure 27, a form of construction is shown in which the upper contacts 16 slide on a tubular member 16a, the contact 16 being carried by the piston 11. scends and strikes an arc and the piston 11 commences to descend, the contacts 16 slide over the member 16a. the contacts 16 never leave it. As shown in the drawings, however, towards thelower part of the 2 stroke of the piston 11, the contacts 16 leave the member 16a so that a second arc Will be struck between them in series with the are between the contacts 7 and 16. The construction may also be slightly modified by arranging for the contact 16 5 never to rise sufficiently to come into contact with the upper contact 16a," in which case, the moving Thus, when the movable contact 7 de- 5 The latter may be made so long that can be squeezedout while the arrangement shown contact 7 passes through in sliding contact with.

in Figure 25 is particularly adapted for easy inspection of two main guiding surfaces 95 and 96 on which the container 2 slides. In Figure 24, the piston 11 is stationary, being fixed to the stationary stem 95 and the upper contacts 16 are also rigidly fixed to that piston. Thus, when the movable contact 7 descends to strike an are between it and the contact 16, the pressure generated by the arc acts on the insulating disc 96 closing the container 2 at the bottom and also has direct access to the underneath surface of the cover 15. The differential pressure, therefore, raises the container 2 against the spring 13, reducing the volume of the space surrounding the contacts 7 and 16 and squeezing oil between the contacts and through the hollow contact 16. This goes on until the container 2 carries the exhaust port 25 above the fixed piston 11 when the pressure above the piston is relieved and the spring 13 is able to return the container 2' into the position shown. If the exhaust is arranged to take place only through the insulator 1 as in Figure 9,

In that case, the first arc is struck 13 In Figures 28-to 30, a series of six units as illustrated in anyone of the preceding figures is shown somewhat diagrammatically in order to indicate the preferred method in which the outlet-or exhaust ports 25 are disposed. There are shown six complete interrupting points providing for two interruptions per phase in a three-phase system. The switch, structures are shown generally at A A for one phase, at B B for the 14c next phase and C C for the third phase. It will be seen that the whole are mounted in pairs in an oil tank 32 of usual construction. the insulator 1 being suspended from the cover 33. haust ports 25 are directed so that products ejected from them will not directly impinge on any other unit of the switch. All of the exhaust ports 25 are directed at angles of 45 degrees to a plane passing through the .central vertical axes of the units A B C Viewed as seen in Figure 30, the g The ex exhaust ports 25 of the units A A, B B are directed forwardly at an angle of 45 degrees and the exhaust ports 25 of the units C C are directed rearwardly at an angle of 45 degrees.

The forms of construction already described may be inverted in a simple fashion under certain conditions, for example, when water or a liquid which has slight conducting'properties is employed as the fluid, it is necessary for the moving contact to be withdrawn entirely from the liquid,

after the arc is extinguished as water tends to conduct if it contains even a trace of impurities. A convenient construction for this purpose which may also be used with other liquids and gases is obtained by making use of a well known method of mounting an outer vessel with an open top and containing the liquid upon an insulator. The other parts are the same except that they are inverted and that the lowermost side of the main piston may be slightly domed to provide a gas trap to act as a buffer if required. The moving 0on tact is withdrawn upwardly out of the enclosure entirely and the are products press the piston in such a direction as to squeeze fluid into the arc gap.

It will be appreciated that theinvention is not limited to the particular examples outlined above, but that the various details of construction may be altered in many directions. Thus, the forms of construction in which the electrode 16 is carried by the moving piston such as shown for example in Figures 3, 7, 9 10, 16, 18 and 23, can with slight modification be arranged for the speed of closing to be increased with increase of current. Thus, if an auxiliary passageway connecting the arcing chamber and the expanding chamber is provided of such a cross section as to allow liquid to be displaced to enable the contacts 16 and .7 to come together in spite of the effect of throttling the passage through the contact 16. In these circumstances, if any arcing takes place just before the circuit breaker is finally closed, the piston carrying the contact 16 is at once moved forward to meet the approaching movable contact 7. Both in such constructions and in forms in which the contact 16 is not carried by the piston, if any arcing takes place during closing of the switch, oil is immediately forced into the arc gap so as to assist in cooling the contact making surfaces.

When a switch, for example, such as shown in Figure 3 is intended to be capable ofthe accelerated closing action upon closing the circuit, the speed of movement of'the movable contact 7 on opening the circuit breaker must be such that with the heaviest currents to be dealt the piston cannot overtake the moving contact.

It is possible to provide for automatic limitation of the length of the arc gap to provide a self-adjusting gap and to arrange for the closing of the switch contacts to be assisted by the arcing and for the pressure to accelerate the closing by regulating an auxiliary opening between the contracting and expanding spaces on opposite sides of the piston so that that opening is only opened during, say the first half inch of the piston stroke so that the throttling effect when the contacts approach close together is not effective in preventing contact during this first portion of the piston stroke, but is effective in regulating the arc gap for the rest of the stroke. Thus, for ex ample, in, the construction shown in Figure 3, one or more small passageways may be provided leading from the upper surface of the piston 11 down in the thickness of the wall of the container 2 and opening to the inside about a half inch above the top edge of the cylinder which extends up from the bottom plate of the container when the piston is in its uppermost position. In such an arrangement even if the passage through the hollow contact 16 becomes throttled by the close approach of the moving contact '7 on closing the circuit breaker, the piston 11 and contact 16 could move towards the moving contact 7 by an amount of a half inch, while during the opening stroke the throttling of the passage through the contact 16 would serve as a controlling factor as soon as the piston had moved down a half inch so as to cover the port or ports in the side wall.

It is possible to minimize an undesirable rise of pressure in. the arcing chamber for example during the high current parts of heavy current waves. For this purpose, openings controlled by the pressure in the arcing chamber may be provided between the arcing chamber and the expanding chamber on the other side of the piston.

Thus, the normal outlet passageway through the contact 16 or through baffle plates, such as are provided in Figures 10, 12, and 21 may be arranged with valve members or obturators as set forth in our United States Patent application Serial No. 596,855 dated 4th March, 1932. Again one or more auxiliary passageways may be provided arranged to open at a predetermined pressure and to give increased opening into the expanding chamber with further increase of pressure. By suitable choice of the sizes of the opening and of the spring control a small movement of a valve may be arranged to provide a wide variation of opening at high frequency.

Another method of avoiding undesirable rise of pressure in the arcing chamber with relatively heavy currents is to provide the arcing chamber with a cushion or yielding piston or pistons opening on one side to the outside of the container 2. Upon occurrence of a high pressure these pistons yield and store energy which is returned to the liquid as the current wave reaches its zero value and oil is squeezed into the arc path. This arrangement does not involve the flow of oil through'parts other than across the contact 16. The springs may be given an initial permanent compression so that the pistons only movebackwards when the pressure rises above a predetermined value. Care should be taken that the total additional volume afforded by those pistons when they are fully compressed is only a small percentage of the volume of the arcing chamber so that the liquid is kept close to the arc stream ready to be driven back into the are at about the time of zero current and so that the arc is not left free to strike on to parts that might be left uncovered by the liquid, if the additional piston volume was relatively larger. A small totally closed bellows containing gas or a spring would be suitable for the purpose.

Yet again fiuid under pressure may be supplied from an external source to the interior of the container 2 to replace the used fluid with clean fluid or to assist the extinguishing action especially at low currents or both in circuit breakers which have to deal with a wide range of current. The fluid will be filled in when required through a non-return valve, the piston or equivalent moving member being conveniently set in motion by or at the time of separation of the electrodes.

In addition to the above, the invention is capable of modification as regardsdetail. It is thus possible to provide a spring co-operating ing parts may be employed. The bellows may have parallel sides or sides diverging or converging towards the arc. In the case of members telescoping within one another increased protection for the main slide member may be obtained by forming it as the inner member and arranging for a flange-like projection of the outer member to slide along it.

In the description above in connection with the drawings, reference has been made to insulating parts, but variations in this direction are possible as the whole or part of the structure may be of insulating material, or again insulating material may be used in other parts to insulate the electrodes from each other while separating and when fully separated.

There have been some references above to the use of seep holes and such holes have been shown and other gas, seep holes are provided to allow the heavier fluid to rise to a predetermined level,

generally depending upon whether it is desired toretain a cushion of the less dense'fluidor to have the whole space or spaces full of the heavier fluid. Generally speaking for a given volume the smaller the cushion in the expanding chamber on one side of the piston, the greater will be the pressure shock which the walls have to withstand and the more quickly will the piston start to move and vice versa.

Where bellows are not employed, one accurately machined guiding surface is in general sufiicient,

provided that the space between the other relatively moving surface through which leakage might occur is kept as small as possible to prevent leakage and the egress of fuse metal beads or burnt material from the arc. The insulating clearances between the metal and the arc can be kept small in circuit breakers constructed in accordance with the invention since the movement of fluid in the arcing chamber takes place from the walls towards the. arc.

Outlet glands should in general be close fitting .to decrease loss of liquid and to increase the efli- I oil to enter the arcing chamber when the piston moves back to its initial position.

To assist adequate clearance in the arcing chamber for a given external container diameter, the movable wall or walls acting to squeeze the contents of .the arcing chamber can be" mounted below and opening into the arcing chamber and may surround the lower part of the moving electrode, being connected by pressure ducts, connecting rods, lazy-tongs, wires passing over pulleys, difierential pulley arrangements and so forth,'with a movable part of the chamber at the other end of the container in which expansionv takes place. Although when the two surfaces are the opposite faces of a piston they are of unequal areas when the surfaces consist of two members 7 coupled together by a pivoted lever or other operative connection, they may be of equal areas if they are carried on unequal lever arms. If a lazy-tongs arrangement of connecting levers is used, the walls can be made to move away from or towards each other, whichever may be a convenient method of arrangement in a given design. Alternatively, in forms of construction such, for example, as that in Figure 1, all'piston movement may be arranged to take place above the solid walled portion of the arcing chamber.

In forms of construction, in which a bellows chamber is arranged to expand towards the leadin insulator during arcing, it is sometimes convenient to use only one upper bellows in which case the current carrying stem which supports the fixed plate or member carrying the fixed electrode may be formed as a wide cage or stirrup, having free space within it for the expansion of the bellows.

In another form of construction utilizing the cage or stirrup, the roof of the expanding chamber or bellows mounted on top of a sold walled arcing chamber has a larger area than that of a plunger piston which it carries on its upper surface and which during arcing is moved upwards so as to compress fluid in a small chamber carried beneath the lead-in insulator from which the fluid under pressure is conveniently fed to squeeze the contents of the arcing chamber by ducts formed in one or more of the bars of the cage or stirrup. I

If a difierent liquid or other fluid is used in the small chamber and ducts than that employed for extinguishing purposes in the arcing chamber, the ducts may be arranged to open'to the-back of a piston or pistons which would therefore be moved to compress the contents of the arcing chamber during arcing. In this case the fluid in the ducts would constitute an example of an operative connection other than by rods or the like. If pistons connected with lever arms are employed, the parts may be arranged to slide in a direction at right angles to the axis of electrode separation, or the pistons subjected to differential pressure may themselves slide at right angles, for example, outside the secondary pressure-retaining chamber and drive oil through passages or ducts in the side walls of the container-into the arcing chamber.

In order to minimize lengthening of the are when the current wave has a high value, grids or a central member of insulating or conducting material may be placed in the passage of the hollow electrode as close to the fluid inlet mouth as will allow full closure of the electrode. The openings in such grids, or the space between a central member and the sides of the hollow electrode are of sufiicient area to allow adequate flow of fluid at high velocity, yet so narrow that a loop of a heavy current are attempting to press through tht 135 opening is short-circuited on itself, and the grids or central member, when of conducting material,

are electrically connected to the electrode with to allow the seating member with its components completely to leave the container when the circuit breaker is fully opened. A bufier spring bearing against a shoulder on the moving contact may be provided to push the seating member 

